In recent years, it has not been rare that a plurality of air-conditioners are installed in home and an electric cooking appliance or appliances of a large capacity are installed in addition thereto or in conjunction therewith. In such a case, an attempt is generally made to increase the allowed current capacity of a power supply line drawn into a house. However, in actual circumstances a measure to increase the allowed current capacity does not match up with an actual total current consumption of electric loads. Namely, there actually results circumstances where a molded-case circuit-breaker may be frequently tripped, leading to service interruption. Although a motor for driving a compressor included in an air-conditioner of these electric loads has a "large capacity load" in which the current consumption is relatively large, there are many instances where such a motor is considered as an "unimportant load" for which an emergency is not so required among home electric loads.
In an apparatus disclosed in the Japanese Laid Open Patent Application (JP-A) No. 201393/1984 publication, a technique is employed to detect a current flowing through a circuit-breaker, i.e., a total current to stop the operation of the air-conditioner so that this total current is not above a trip current value, or to successively stop one by one, when a plurality of air-conditioners are installed, these air-conditioners accordingly as the total current becomes equal to a trip current value of the circuit-breaker. However, once the air-conditioner is stopped, even if such a stop is a temporary stop, it would take much time for restarting, and even if the air-conditioner is restarted, it cannot immediately exhibit air-conditioning capability or ability. For this reason, there are problems from both viewpoints of the air-conditioning effect and energy conservation or saving.
On the other hand, in an apparatus disclosed in the Japanese Laid Open Patent Application (JP-A) No. 211659/1986 publication, a technique is employed to effect a control such that when a total current becomes equal to the trip current value of a circuit-breaker, a drive frequency of a compressor of a specific air-conditioner is lowered, and to further effect a control to detect that the total current is lowered to a predetermined value by the above control to increase the drive frequency so that it becomes in correspondence with the original frequency for a second time. Accordingly, since the compressor is not easy to be stopped, the problems of the air-conditioning effect and the energy conservation or saving are difficult to take place. However, in the case where a plurality of such air-conditioners are installed and are operated at the same time, unless current detection levels of all the air-conditioners are in correspondence with each other, the capability or ability of only an air-conditioner having the highest current detection level is lowered. As a result, that air-conditioner would be eventually stopped. In this case, similarly to the technology described in the above referenced Japanese Laid Open Application (JP-A) No. 201393/1984, the air-conditioner is once stopped. This is a problem from the viewpoints of the air-conditioning effect and the energy conservation or saving.
Further, in the case where current detection levels of all plural air-conditioners installed are assumed to be the same although this is not realistic, when a total current becomes close to a trip current of the circuit-breaker, the capabilities or abilities of all the air-conditioners being operated are caused to be lowered. As a result, the total current is lowered to a great degree as compared to the trip current of the circuit-breaker. At this time, the capabilities of respective air-conditioners are increased or enhanced. In this case, since the capabilities of a plurality of air-conditioners are increased or enhanced at the same time, the total current increases for a second time. As a result, the capabilities of all the air-conditioners being operated are caused to be lowered for a second time, resulting in a state where the above operation is repeatedly conducted. This state is an entirely unstable state. This constitutes a cause to hasten consumption of equipments and to shorten the life time.